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Fracture Simulation of Electrofusion Joining.
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
2015 (English)Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This Master thesis investigates mechanical failures of electrofusion joints. This type of joints are used for weld high density polyethylene pipe systems where tting and pipe will be welded together by the heat caused by the resistance of the copper cables to electric current. There have been some failures where a brittle crack has grown through the fusion zone. Polyethylene as a material has a ductile character but brittle behavior occurs due to an unsuccessful welding by a poor fusion interface. In this study, we have chosen to investigate the plausible load cases that can cause the failure and studied the e ect of the geometry of the tting on the fracture toughness of the welded structure. We used the nite element method numerical analysis. We have approached unsuccessful welding (brittle) with a linear model and non-linear (CZM) model and successful welding (ductile) with a non-linear XFEM model. The material parameters needed for these models are gathered by series of experiments. The results shows that the inside pressure is the critical load case. The linear model and CZM model are consistent in terms of predicted responses to the geometrical parameters for the unsuccessful welding. Decreasing the inner cold zone length, increasing the fusion length and the thickness of the tting will improve the fracture toughness of the welded structure.

Abstract [sv]

Detta examensarbete på masternivå handlar undersökning och simulering av brott i elektromuffsvetsar. Den har typen av svets används för att sammansvetsa rör  av högdensitiets polyeten där muff och rör svetsas samman med värmen som skapas på grund av koppartråadens motstånd mot elektrisk ström. Flera tidiga brott där en spröd spricka har växt genom svetsområdet har observerats. Polyeten som material ar duktilt men sprött beteende förekommer på grund av dålig svets och svetsgränssnitt.

I detta arbete valdes att undersöka de möjliga kritiska belastningar som kan orsaka brott och påverkan av muffens geometri på brottmotstandet hos den ihopsvetsade muff- och rörstrukturen. Den numeriska finita element-metoden användes. En dålig svets (spröd) angreps med en linjar modell och en icke linjar (CZM) modell och en bra svets (duktil) hanterades med en icke linjäar (XFEM) modell. Aktuella materialparametrar identiferades genom experiment. Resultatet visar att det inre trycket är den kritiska belastningen. I termer av respons till de geometriska parametrarna, var den linjära och icke-linjära modellen (CZM) for den dåliga svetsen konsekventa. Reducerad inre kylzon, ökning av svetslängd, och öokning av mufftjocklek ökar brottmotståndet hos den ihopsvetsade strukturen.

Place, publisher, year, edition, pages
2015. , 64 p.
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-177363OAI: oai:DiVA.org:kth-177363DiVA: diva2:872575
External cooperation
Swerea KIMAB
Subject / course
Solid Mechanics
Supervisors
Examiners
Available from: 2015-11-26 Created: 2015-11-19 Last updated: 2015-11-26Bibliographically approved

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CiteExportLink to record
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